"Wet" vs "Dry" Filter elements

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

bstoner59

does it come in shmedium?
Joined
Jul 13, 2010
Posts
6,104
Reaction score
4,753
Location
Orange, CA
I realize now that there is a great divide in the Raptor world as to which filter elements work best...oiled or dry elemnts.

Here's my .02 based on my amount of OFFROAD driving...

I have grown up riding and racing dirt bikes. From the time I was old enough to ride (4 yrs old) I remember cleaning and oiling my air filters. Everyone in the dirt bike community does it.

The air box on most bikes is located right above the rear wheel under the seat. In this location a lot of dust is swirled around the filter element. If there was no oil on the filter these fine dust particles would get thorugh to the carb down into the engine etc. These filters aren't perfect (kind of like a sponge w/ oil) and sand dirt and dust will get through over the years esp if not cleaned on a regular basis (which will also lead to clogging of the filter).

One of the big concerns in the automotive community from what I gather is that oil can pass from the filter to the engine etc. I know on my motorcycles the inner airbox is designed to allow oil to pool up in a lower compartment and I'm sure some does go into the engine. Remeber these are hand oiled 'sponges'.

The K&N elements are a lot more intricate than these old motorcycle designs and the oil is sprayed onto the outer layer of the element. The oils used for air filters a re VERY tacky, almost like a glue. They are designed to be adhesive to filters, dust or anything that touches it. If the tiny amount that is sprayed onto the element was to seap through my bet is that it would have a difficult time traveling all the way to the engine.

Let's say there is a choice to have oil or dirt pass through to the engine...what would you prefer? I personally would take the small amount of oil over a small amount of dirt.


Brian
 

MagicMtnDan

FRF Addict
Joined
Oct 28, 2011
Posts
7,661
Reaction score
1,793
Location
Magic Mountain
Hmmm. This is not my area of expertise at all. That said, I will submit to you that I'm not sure those are the only choices. Your statement assumes that using a dry, paper filter will allow a small amount of dirt into the engine. Now that may be true but I submit to you (two submissions in one paragraph - probably a no-no) that if that is the case then the Ford engineers designed it that way so it must be OK. I say that because (1) the Raptor was designed to be driven offroad and (2) its air filter system was designed to allow the Raptor to be driven offroad.

Is there something wrong with this logic?
 

BigJ

FRF Addict
Joined
Aug 5, 2010
Posts
5,448
Reaction score
1,559
As an aside, dry doesn't necessarily mean paper. In fact, I don't think you'll find any aftermarket (serviceable) dry filter that's paper. Typically they'll use a synthetic blend of fiberglass, cotton, wool and/or polyester.

My experience says that the day of the dry filter is here. Manufacturing techniques exist today that allow for a much denser pleat pattern that is often deeper as well; more surface area means more filtration ability. And the media itself is constructed to flow far more air than our engines need. So as they collect dust and dirt, the necessary air just reroutes around the clogged fibers. This means that the engine still gets all the air it needs.

Or to put it another way, an oil filter might perform as well as a dry filter when new (or freshly serviced), but their flow abilities decrease sooner than a quality dry filter as the miles pile up and they "load up".

And, of course, cleaning a dry is much less involved than cleaning an oil. Most quality drys are hydrophobic; they don't absorb water. So its literally a rinse shake out and run, rather than rinse, then let dry, then oil, then let dry, then run.

I don't have any flow bench data to back this up. Its just what I've seen reported over recent years regarding this subject. Hey, maybe we ought to get a flow bench and try this stuff out...

:)
 

MarkT

FRF Addict
Joined
Mar 4, 2010
Posts
1,202
Reaction score
26
Hey Brian... we have similar backgrounds with dirt bikes... except I remember the days when they came with PAPER filters!

Here's the history of the "oiled filter" in regards to dirt bikes as I lived it:

Paper filters were the standard in the early days of motocross bikes. But there was a problem. If a paper filter got wet, if it didn't tear, it swelled up and no more air would flow. Even if it dried out, it was damaged would not flow properly. But paper filters did keep the dirt out!

Most dirt bikes in the 1960's were two strokes of the "piston port" design... without boring you with the details of operation, the result was that at low rpm a LOT of the air/fuel/oil mixture was spit back through the carburetor...

In those days, the foam rubber available would be attacked by oil... and the fog of fuel made things even worse. The foam would break down over time and the filter would become very restrictive.

In the late 60's, K&N in Riverside, CA came up with the "oiled gauze" idea for two-stroke off road dirt bikes... Gauze did not break down like the foam of the day, flowed a lot of air, and wasn't affected by getting wet... oiled gauze did not filter as well as paper in those days... but it was a great option in the day.

In the early 70's, new kinds of foam were available and most bikes had some sort of oiled foam filter. But you still had to replace the foam filter every year or two. Some brands would literally disintegrate if washed in strong solvent or even gasoline. K&N's were better in this respect as well.

As I remember it, the paper filter was the best when it came to filtering. But paper wasn't great on motorcycles used off road in wet conditions... and the "spit back" through the carb didn't help either.

I've used K&N filters off road for years... decent filter. But they do let some of the fine silt through especially when new. (A K&N actually filters better when dirty... as long as you don't let it dry out.) I usually used a K&N with a foam prefilter...

As has been mentioned, "paper" filters have come a long way. The quality ones are now made out of synthetic materials and are a good choice in my opinion... especially when it comes to keeping the dirt out. (some "paper" filters... like the one in the Raptor... are even "oiled".)
 

FSM06

Full Access Member
Joined
Aug 13, 2010
Posts
853
Reaction score
17
Location
Colorado
Another thing that comes to mind in my experience with diagnosing driveability concerns dealing with "wet" filters is that small amounts of the oil (usually caused by over-oiling) travel through the element and adhere to the hot wire of the Mass Air Flow sensor negatively affecting its ability to accurately calculate air flow into the engine. The PCM interprets this as a lean condition and increases the fuel injector pulse width (or in simpler terms, adds fuel) decreasing fuel economy and eventually flagging a check engine light.
 
Top